1. Field of the Invention
The present invention relates to a feed/transport roller (i.e., a roller for feeding or transporting sheet material) for use in a variety of OA (office automation) machines such as copying machines, facsimiles, and printers.
2. Background Art
Conventionally, feed/transport rollers for use in a variety of OA machines have been required to have excellent sheet transportation capacity and wear resistance. To meet this requirement, such rollers are conventionally formed from EPDM (ethylene-propylene-diene rubber), which has excellent mechanical strength and high friction coefficient.
However, the friction resistance of EPDM is no longer satisfactory in view of recent trends in OA machines; i.e., extension of service life and increase in operation speed.
Meanwhile, studies are also carried out on use of urethane-based material having excellent friction resistance as a material for producing feed/transport rollers.
However, since urethane-based material having low hardness is difficult to produce, the resultant roller tends to exhibit poor feeding performance. Specifically, the hardness of castable urethane material cannot be lowered to a value lower than 50° as measured by means of a durometer (JIS A type). If the hardness is lowered beyond the lower limit, the urethane material will no longer be usable, due to its poor durability.
Feed rollers can also be formed from a millable urethane material. Japanese Patent Application Laid-Open (kokai) No. 11-5637 discloses that a feeding roller is produced from an ε-caprolactone-based polyurethane having excellent hydrolysis resistance and mechanical strength. However, when the hardness of the polyurethane is lowered, friction resistance also decreases to a level which is not suitable for practical use.
Feed/transport rollers, particularly feed rollers for use in a sheet-feeding member, are required to have low hardness and high impact resilience for attaining satisfactory sheet feeding capacity, as well as to have durability.